The present invention relates to a sheet metal member that is formed into a shape in which a flange portion is projected outward integrally around the whole periphery of a cylindrical boss portion, and that can be used as, for example, a housing lower part of a gas generator of an air bag for an automobile, and also to a method of producing the member.
Conventionally, it is well known that a sheet metal member of the shape having: a cylindrical boss portion; and a flange portion which is projected outward integrally around the whole periphery of the boss portion is obtained by using a thin disk-like blank. However, there exists no sheet metal member in which an inward collar is raisedly shaped by an ironing process on the inner periphery of an axial intermediate portion of the boss portion of the sheet metal member, and no processing technique for it.
It is an object of the invention to provide a sheet metal member in which an inward collar is raisedly shaped by an ironing process on the inner periphery of an axial intermediate portion of a cylindrical boss portion of such a sheet metal member of the shape wherein a flange portion projects outwardly and integrally around the entire periphery of the boss portion, and also a method of producing the member.
It is another object of the invention to provide a sheet metal member which presents such a shape, which is light, and which is durable.
It is a further object of the invention to provide a production method in which a sheet metal member presenting such a shape can be easily produced in steps the number of which is as small as possible, at a low cost, and with forming no cut chip so as to reduce the material.
The sheet metal member of the invention is a sheet metal member having: a cylindrical boss portion; and a flange portion which is projected outward integrally around a whole periphery of the boss portion, and characterized in that an inward collar is shaped on an inner periphery of an axial intermediate portion of the boss portion, the inward collar being raised toward an axial center by thinly ironing an inner peripheral wall of the boss portion.
The thus configured sheet metal member is light and has good durability.
The method of producing a sheet metal member of the invention is characterized in that the method comprises the steps of: shaping a semifinished product from a thin disk-like blank, the semifinished product having a cylindrical boss portion, and a flange portion which is projected outward integrally around a whole periphery of the boss portion; and clampingly holding the semifinished product between a top pattern tool which has an ironing punch at a center in a vertically movable manner, and a bottom pattern tool which has similarly an ironing punch at a center in a vertically movable manner, and thinly ironing an inner peripheral wall of the boss portion by pressingly inserting the ironing punch of the top pattern tool into the boss portion from an upper side, and the ironing punch of the bottom pattern tool into the boss portion from a lower side, whereby an inward collar is raisedly shaped toward an axial center on an inner periphery of an axial intermediate portion of the boss portion.
Preferably, an ironing process of shaping the inward collar is repeated several times to finish the inward collar of a final shape.
According to this production method, a sheet metal member in which an inward collar is shaped on the inner periphery of the axial intermediate portion of the boss portion can be easily obtained by an ironing process using a thin disk-like blank and the ironing punches of the top and bottom pattern tools, in a reduced number of steps, at a low cost, and with forming no cut chip to economically use the material.